The period of 1 to 3 months is interesting to study, she says. Infants aren't mobile and they're gaining a lot of information about the world – especially coming up with preferences for people who look like them. "1 to 3 months is the earliest age when we're starting to look at preferences for faces," Even a few hours old, babies prefer their mother's face over other types of faces. But before 6 months, babies don't show a preference for faces of their own race over other races, while later on they do. "We want to know how they learn the preference," says Sugden. Looking at faces helps the baby brain develop, but the trick is figuring out exactly how.